That massive lead poisoning causes gross abnormalities of brain and behavior has been recognized for many years. But only recently have studies of pediatric plumbism led many workers to suggest that relatively mild chronic exposures to lead, particularly if they occur from birth to about seven years of age, may produce permanent brain damage characterized by more subtle intellectual, emotional and perceptual-motor disorders. Systematic experimental studies of the effects of low level chronic exposure to lead during the developmental period have not been possible in humans and have not been attempted in animals. In the studies proposed here we will use rats which have been exposed from birth to low levels of lead; we have already established that such animals do not display gross brain damage but do develop abnormal behavior patterns such as hyperactivity, aggressiveness, and repetitive movements. In these experiments, newborn rats will be fed a lead-containing diet to simulate pica. Our primary goal throughout these experiments will be to quantify, and correlate, if possible, (a) brain lead concentrations, (b) concentrations of brain monoamines, (c) spontaneous activity, and (d) learning ability. These parameters will be followed in three different basic sets of experiments; (1) the first, and fundamental, experiment will determine the effects of low level lead exposures beginning at birth and continuing for the duration of the experiment, (2) in other experiments lead exposure will begin at weaning or later to establish the relative effects of lead at different developmental stages, (3) finally, to determine whether recovery from the effects of lead occur, observations will be made at various periods of time after termination of lead exposure.